Rapid and damage-free outgassing of implanted helium from amorphous silicon oxycarbide

In-Situ TEM Investigation of Helium Implantation in Ni-SiOC Nanocomposites

Ni-SiOC nanocomposites maintain crystal-amorphous dual-phase nanostructures after high-temperature annealing at different temperatures (600 °C, 800 °C and 1000 °C), while the feature sizes of crystal Ni and amorphous SiOC increase with the annealing temperature. Corresponding to the dual-phase nanostructures, Ni-SiOC nanocomposites exhibit a high strength and good plastic flow stability. In this study, we conducted a He implantation in Ni-SiOC nanocomposites at 300 °C by in-situ transmission electron microscope (TEM) irradiation test. In-situ TEM irradiation revealed that both crystal Ni and amorphous SiOC maintain stability under He irradiation. The 600 °C annealed sample presents a better He irradiation resistance, as manifested by a smaller He-bubble size and lower density. Both the grain boundary and crystal-amorphous phase boundary act as a sink to absorb He and irradiation-induced defects in the Ni matrix. More importantly, amorphous SiOC ceramic is immune to He irradiation damage, contributing to the He irradiation resistance of Ni alloy.

Radiation Effects in the Crystalline-Amorphous SiOC Polymer-Derived Ceramics: Insights from Experiments and Molecular Dynamics Simulation

Radiation-tolerant materials are in great demand for safe operation and advancement of nuclear and aerospace systems. Nanostructuring is a key strategy to improve the radiation tolerance of materials. SiOC polymer-derived ceramics (PDCs) are unique synthetic nanocomposites consisting of β-SiC nanocrystals and turbostratic graphite distributed in amorphous SiOC matrix, which are "all-rounder" materials for many advanced structural and functional applications. Radiation effects in the crystalline-amorphous system have been investigated in detail by experiments and molecular dynamics (MD) simulations. The results indicate that the amorphous SiOC structure retains amorphous accompanied by redistribution of the Si-containing tetrahedra. The graphite is shown to amorphize more easily than β-SiC nanocrystals under the same irradiation condition. The sample richer in oxygen, namely, containing more amorphous SiOC, shows less disordering of graphite, resulting from greater mitigation of radiation damage by the amorphous phase as efficient sinks. This study provides details of the microstructure evolution of SiOC PDCs under ion irradiation, as well as insights for the design and development of advanced ion damage-resistant materials.

Mechanical Response of He-Implanted Amorphous SiOC/Crystalline Fe Nanolaminates

This study investigates the microstructural evolution and mechanical response of sputter-deposited amorphous silicon oxycarbide (SiOC)/crystalline Fe nanolaminates, a single layer SiOC film, and a single layer Fe film subjected to ion implantation at room temperature to obtain a maximum He concentration of 5 at. %. X-ray diffraction and transmission electron microscopy indicated no evidence of implantation-induced phase transformation or layer breakdown in the nanolaminates. Implantation resulted in the formation of He bubbles and an increase in the average size of the Fe grains in the individual Fe layers of the nanolaminates and the single layer Fe film, but the bubble density and grain size were found to be smaller in the former. By reducing the thicknesses of individual layers in the nanolaminates, bubble density and grain size were further decreased. No He bubbles were observed in the SiOC layers of the nanolaminates and the single layer SiOC film. Nanoindentation and scanning probe microscopy revealed an increase in the hardness of both single layer SiOC and Fe films after implantation. For the nanolaminates, changes in hardness were found to depend on the thicknesses of the individual layers, where reducing the layer thickness to 14 nm resulted in mitigation of implantation-induced hardening.

Resistance to Helium Bubble Formation in Amorphous SiOC/Crystalline Fe Nanocomposite

The management of radiation defects and insoluble He atoms represent key challenges for structural materials in existing fission reactors and advanced reactor systems. To examine how crystalline/amorphous interface, together with the amorphous constituents affects radiation tolerance and He management, we studied helium bubble formation in helium ion implanted amorphous silicon oxycarbide (SiOC) and crystalline Fe composites by transmission electron microscopy (TEM). The SiOC/Fe composites were grown via magnetron sputtering with controlled length scale on a surface oxidized Si (100) substrate. These composites were subjected to 50 keV He+ implantation with ion doses chosen to produce a 5 at% peak He concentration. TEM characterization shows no sign of helium bubbles in SiOC layers nor an indication of secondary phase formation after irradiation. Compared to pure Fe films, helium bubble density in Fe layers of SiOC/Fe composite is less and it decreases as the amorphous/crystalline SiOC/Fe interface density increases. Our findings suggest that the crystalline/amorphous interface can help to mitigate helium defect generated during implantation, and therefore enhance the resistance to helium bubble formation.